﻿<%@ WebHandler Language="C#" Class="ValidateCode" %>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Drawing;
using System.Web.SessionState;
/// <summary>
/// ValidateCode 的摘要说明
/// </summary>
public class ValidateCode : IHttpHandler, IRequiresSessionState
{

    public void ProcessRequest(HttpContext context)
    {
        ///特别注意，如不加，单击验证图片’看不清换一张’，无效果．
        context.Response.Cache.SetCacheability(HttpCacheability.NoCache);
        this.CreateCheckCodeImage(GenerateCheckCode(context), context);
    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
    private string GenerateCheckCode(HttpContext context)
    {
        int number;
        char code;
        string checkCode = String.Empty;
        System.Random random = new Random();

        for (int i = 0; i < 4; i++)
        {
            number = random.Next();
            if (number % 2 == 0)
            {
                code = (char)('0' + (char)(number % 10));
            }
            else if (number % 3 == 0)
            {
                code = (char)('A' + (char)(number % 26));
            }
            else
            {
                code = (char)('a' + (char)(number % 26));
            }
            checkCode += code.ToString();
        }
        context.Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));
        //你也可以存到Seesion里
        context.Session["CheckCode"] = checkCode;
        return checkCode;
    }

    private void CreateCheckCodeImage(string checkCode, HttpContext context)
    {

        if (checkCode == null || checkCode.Trim() == String.Empty)
        {
            return;
        }
        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
        Graphics g = Graphics.FromImage(image);

        try
        {
            //生成随机生成器
            Random random = new Random();
            //清空图片背景色
            g.Clear(Color.White);
            //画图片的背景噪音线
            for (int i = 0; i < 25; i++)
            {
                int x1 = random.Next(image.Width);
                int x2 = random.Next(image.Width);
                int y1 = random.Next(image.Height);
                int y2 = random.Next(image.Height);
                g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
            }

            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
            g.DrawString(checkCode, font, brush, 2, 2);

            //画图片的前景噪音点
            for (int i = 0; i < 100; i++)
            {
                int x = random.Next(image.Width);
                int y = random.Next(image.Height);
                image.SetPixel(x, y, Color.FromArgb(random.Next()));
            }

            //画图片的边框线
            g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            context.Response.ClearContent();
            context.Response.ContentType = "image/Gif";
            context.Response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }
}